A vendor on Peachtree sells bratwurst hot dogs for $4.10. His cart is open from 9 - 5, Monday through Friday. His variable costs average $0.70 per hot dog (depending mostly on toppings). He is considering making a couple of changes to his operation. First, he is going to upgrade both the hot dogs and the condiments, which will increase variable costs by $0.34. He is also considering a price increase to $4.80. Calculate the percent profit breakeven metric, with a change in variable cost, for the proposed changes. Report your answer as a percentage (whole number) and round to the nearest percentage point.

The correct answer is -10

Can you please explain how -10 is the correct answer? Thank you.